Level densities and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>γ</mml:mi></mml:mrow></mml:math>-ray strength functions in Sn isotopes

Toft, H. K.; Larsen, A. C.; Agvaanluvsan, U.; Bürger, A.; Guttormsen, M.; Mitchell, G. E.; Nyhus, H. T.; Schiller, A.; Siem, S.; Syed, N. U. H.; Voinov, A.

doi:10.1103/physrevc.81.064311

Cited by 59 publications

(75 citation statements)

References 37 publications

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“…Even if the back-shifted Fermi-gas formula gives rather good descriptions for the level densities of some nuclei [28], it does not reflect the expected change in the heat capacity and thus in the slope of the level-density curve at the critical pairing energy, see the discussion on the nuclear temperature below. Moreover, the use of the Fermi-gas formula that is valid in the independent-particle picture in an energy range where pairing correlations are present is a severe inconsistency.…”

Section: Back-shifted Fermi-gas Modelmentioning

confidence: 99%

Inconsistencies in the description of pairing effects in nuclear level densities

Schmidt

Jurado

2012

Phys. Rev. C

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Pairing correlations have a strong influence on nuclear level densities. Empirical descriptions and theoretical models have been developed to take these effects into account. The present article discusses cases, where descriptions of nuclear level densities are inconsistent or in conflict with the present understanding of nuclear properties. Phenomenological approaches consider a back-shift parameter. However, the absolute magnitude of the back-shift, which actually corresponds to the pairing condensation energy, is generally not compatible with the observation that stable pairing correlations are present in essentially all nuclei. It is also shown that in the BCS model pairing condensation energies and critical pairing energies are inconsistent for light nuclei. A modification to the composite Gilbert-Cameron level-density description is proposed, and the use of more realistic pairing theories is suggested.

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Section: Back-shifted Fermi-gas Modelmentioning

confidence: 99%

Inconsistencies in the description of pairing effects in nuclear level densities

Schmidt

Jurado

2012

Phys. Rev. C

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“…For the illustration we have selected some nuclei for which the dipole RSF have been studied recently and reported in Refs. [11,28,29] Sn calculated within the TCQRPA at finite and zero temperatures, compared to data. To be specific, in this work we consider the nuclear excitation energy E * equal to the neutron separation energy E * = S n .…”

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confidence: 99%

Low-energy limit of the radiative dipole strength in nuclei

Литвинова

Белов

2013

Phys. Rev. C

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We explain the low-energy anomaly reported in several experimental studies of the radiative dipole strength functions in medium-mass nuclei. These strength functions at very low gamma-energies correspond to the gamma-transitions between very close nuclear excited states in the quasicontinuum. In terms of the thermal mean-field, the low-energy enhancement of the strength functions in highly-excited compound nuclei is explained by nucleonic transitions from the thermally unblocked single-quasiparticle states to the single-(quasi)particle continuum. This result is obtained within the finite-temperature quasiparticle random phase approximation in the coordinate space with exact treatment of the single-particle continuum and exactly eliminated spurious translational mode. The case of radiative dipole strength functions at the nuclear excitation energies typical for the thermal neutron capture is illustrated for 94,96,98 Experimental and theoretical studies of the nuclear low-energy electric dipole response remain among the challenges of the modern nuclear structure physics and attract an increasing interest because of its astrophysical impact. Radiative strength (γ-strength) at low energies may enhance the neutron capture rates in the r-process of nucleosynthesis [1, 2] with a considerable influence on elemental abundance distributions. One of the key phases of the r-process nucleosynthesis is capture of a thermal neutron with the subsequent γ-decay of the compound nucleus. The typical neutron energy in the astrophysical plasma is about 100 keV. Therefore, the description of γ-emission spectra of a compound nucleus with excitation energies of the order of the neutron separation energy is the central problem. Hauser-Feshbach model is a standard tool for calculations of the radiative neutron capture cross sections [3]. Formally, this model includes all possible decay channels via transmission coefficients. In the gamma-decay channel the corresponding coefficient is determined by the radiative strength function which is usually calculated by one of the phenomenological parameterizations [4][5][6]. However, in more recent works [1,2,7] it has been shown that for the most important electric dipole strength these simple models are not sufficient because they do not account for structural details of the strength at the neutron threshold. Sensitivity of the stellar reaction rates to these details emphasizes the importance of their studies within microscopic selfconsistent models.Another key ingredient for the Hauser-Feshbach calculations is the Brink-Axel hypothesis [8] stating that the γ-strength does not depend on the nuclear excitation energy, in particular, it is the same for excited and nonexcited nuclei. Supposedly true for the giant resonances and for the soft modes like pygmy dipole resonance, this hypothesis is, however, violated for the lowest transition energies. For instance, non-zero strength is systematically observed at very low gamma-energies [9]. Radiative strength functions extracted from various measurem...

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“…In a simple macroscopic picture, a displacement of center-of-mass and center-ofcharge of the nucleus generates a vibrational motion trying to restore the proton-neutron symmetry. Nowadays, the rapidly increasing number of experiments using different probes and techniques allow for systematic studies of the PDR over isotopic and isotonic chains from different mass regions [4,[7][8][9][10][11][12][13][14][15][16][17]. A close connection between * derya@ikp.uni-koeln.de the total PDR strength and the amount of the neutron excess of neutron-rich nuclei which on the other hand is correlated with the neutron skin thickness was proposed [6,[18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Decay of quadrupole-octupole1−states inCa40andCe140
Derya
¹
,
Tsoneva
²
,
Aumann
³

et al. 2016
Phys. Rev. C
12
1
2
0
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Level densities andγ-ray strength functions in Sn isotopes

Cited by 59 publications

References 37 publications

Inconsistencies in the description of pairing effects in nuclear level densities

Inconsistencies in the description of pairing effects in nuclear level densities

Low-energy limit of the radiative dipole strength in nuclei

Decay of quadrupole-octupole1−states inCa40andCe140
Derya
¹
,
Tsoneva
²
,
Aumann
³

et al. 2016
Phys. Rev. C
12
1
2
0
View full text Add to dashboard Cite

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Level densities andγ-ray strength functions in Sn isotopes

Cited by 59 publications

References 37 publications

Inconsistencies in the description of pairing effects in nuclear level densities

Inconsistencies in the description of pairing effects in nuclear level densities

Low-energy limit of the radiative dipole strength in nuclei

Decay of quadrupole-octupole1−states inCa40andCe140Derya1, Tsoneva2, Aumann3 et al. 2016Phys. Rev. C12120View full textAdd to dashboardCite

Contact Info

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About

Decay of quadrupole-octupole1−states inCa40andCe140
Derya
¹
,
Tsoneva
²
,
Aumann
³

et al. 2016
Phys. Rev. C
12
1
2
0
View full text Add to dashboard Cite